tehbeard · June 3, 2024 18:21
diff --git a/gex-decompiler.html b/gex-decompiler.html
 <!DOCTYPE html>
 <html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>GameMaker 7/8.1 GEX decompiler</title>
  </head>
  <body>
    <h1>GameMaker 7/8.1 GEX decompiler</h1>
    <p>
      <strong>What the hell is this?</strong>
      <br/>
      I found a GameMaker 8.1 project of mine, and wanted to open it in Game Maker Studio 2.0.<br/>
      You can't natively import <code>.gmk</code> files into GMS2. <br/>
      I used <a href="http://lateralgm.org/">LateralGM</a> to get the project into a GMS1 compatible format.
      <br/><br/>
      Unfortunately this doesn't seem to handle extension packages. (A mechanism for reusable code)<br/>
      And GMS1/2 doesn't handle <code>.gex</code> files.<br/>
      So, I wrote this decompiler to get the code out of a <code>.gex</code> file so I could get the project to compile in GMS2.
    </p>
    
    <p>
      <strong>References I used in building this.</strong><br/>
      <a href="https://enigma-dev.org/docs/Wiki/GMKrypt">https://enigma-dev.org/docs/Wiki/GMKrypt</a><br/>
      <a href="http://lateralgm.org/formats/gmkrypt1.html">http://lateralgm.org/formats/gmkrypt1.html</a><br/>
      <a href="https://github.com/IsmAvatar/LateralGM">https://github.com/IsmAvatar/LateralGM</a><br/>
      <a href="https://enigma-dev.org/docs/Wiki/GEX_format">https://enigma-dev.org/docs/Wiki/GEX_format</a><br/>
      <a href="https://enigma-dev.org/docs/Wiki/GED_format">https://enigma-dev.org/docs/Wiki/GED_format</a><br/>
    </p>
    <p>
      This madness is all <a href="https://develop.games/" target="_blank">Thor's fault.</a>
    </p>
    <hr/>
    <input type="file" id="gex" accept=".gex" />

    <script type="module">
      // This code only exists because Thor is a meance of postivity towards making games.

      // GMKrypyt code
      // https://enigma-dev.org/docs/Wiki/GMKrypt
      // http://lateralgm.org/formats/gmkrypt1.html

      function generateSwapTable(seed) {
        const table = [[], []]; // int[][] table = new int[2][256];

        const a = 6 + (seed % 250);
        const b = Math.floor(seed / 250);

        for (let i = 0; i < 256; i++) {
          table[0][i] = i;
        }

        for (let i = 1; i < 10001; i++) {
          const j = 1 + ((i * a + b) % 254);
          const t = table[0][j & 0xff];
          table[0][j] = table[0][j + 1] & 0xff;
          table[0][j + 1] = t & 0xff;
        }
        table[1][0] = 0; //this operation is optional, as 0 is default
        for (let i = 1; i < 256; i++) {
          table[1][table[0][i]] = i & 0xff;
        }
        return table;
      }

      export function decryptGMKrypt(seed, data) {
        const lookup = generateSwapTable(seed);

        return data.map((byte) => lookup[1][byte] & 0xff);
      }

      // GEX File format decompiler
      // https://github.com/IsmAvatar/LateralGM
      // https://enigma-dev.org/docs/Wiki/GED_format#cite_note-extdef-1
      export async function decompile(data) {
        const view = new DataView(data.buffer);

        const formatId = view.getInt32(0, true);
        const version = view.getInt32(4, true);

        // const seedPre = view.getInt32(8, true);
        // const seedPost = view.getInt32(12, true);

        const seed = view.getInt32(8, true);

        const plaintext = decryptGMKrypt(seed, data.slice(12));
        // Parse the GED
        const txtDec = new TextDecoder();

        const plainView = new DataView(plaintext.buffer);

        function readPrefixedString() {
          const size = plainView.getUint32(gedOffset, true);
          const value = txtDec.decode(
            plaintext.subarray(gedOffset + 4, gedOffset + 4 + size)
          );
          gedOffset += 4 + size;
          return value;
        }

        function readUInt32() {
          const value = plainView.getUint32(gedOffset, true);
          gedOffset += 4;
          return value;
        }
        let gedOffset = 0;

        const gedVersion = readUInt32();
        const editable = readUInt32();

        const labels = [
          "Name",
          "Folder",
          "Version",
          "Author",
          "Date",
          "License",
          "Description",
          "Help File",
        ];
        const metadata = {};

        for (const label of labels) {
          const value = readPrefixedString();
          metadata[label] = value;
        }

        const hidden = readUInt32(); // Skip hidden

        // Uses
        const usesCount = readUInt32();
        const uses = [];
        for (let i = 0; i < usesCount; i++) {
          uses.push(readPrefixedString());
        }

        // Files
        const filesCount = readUInt32();
        const files = [];
        const fileTypes = ["N/A", "DLL", "gml", "Action Library", "Other"];
        const callCon = { 2: "GML", 11: "stdCall", 12: "cdecl" };
        for (let i = 0; i < filesCount; i++) {
          const version = readUInt32();

          const fileName = readPrefixedString();

          const originalName = readPrefixedString();

          const kind = fileTypes[readUInt32()];

          const initialization = readPrefixedString();

          const finalization = readPrefixedString();

          const functionCount = readUInt32();

          const functions = [];
          for (let i = 0; i < functionCount; i++) {
            const version = readUInt32();
            const name = readPrefixedString();
            const ext_name = readPrefixedString();
            const call_con = callCon[readUInt32()];
            const helpLine = readPrefixedString();
            const hidden = readUInt32();
            const argCount = readUInt32();

            gedOffset += 4 * 18;

            functions.push({
              version,
              name,
              ext_name,
              call_con,
              helpLine,
              hidden,
              argCount,
            });
          }

          const constantCount = readUInt32();

          const constants = [];
          for (let i = 0; i < constantCount; i++) {
            const version = readUInt32();
            const name = readPrefixedString();
            const value = readPrefixedString();
            const hidden = readUInt32();
            constants.push({
              version,
              name,
              value,
              hidden,
            });
          }

          files.push({
            version,
            fileName,
            originalName,
            kind,
            initialization,
            finalization,
            functions,
            constants,
          });
        }

        async function readCompressedDat()
        {
          const datSize = readUInt32();
          const datCompressed = plaintext.slice(gedOffset, gedOffset + datSize);
          gedOffset += datSize;

          const unzip = new DecompressionStream("deflate");
          const writer = unzip.writable.getWriter();
          writer.write(datCompressed);
          writer.releaseLock();

          const reader = unzip.readable.getReader();

          const read = await reader.read();
          return read.value;
        }

        for(let file of files)
        {
          file.data =  await readCompressedDat();
          file.dataText = txtDec.decode(file.data);
        }

        console.log({
          gedVersion,
          editable,
          hidden,
          metadata,
          files
        });



        // const datSeed = readUInt32();
        // console.log("datSeed:", datSeed);

        // console.log( gedOffset + datSize , plaintext.length);


        // console.log(unzip.length);

        return {
          gedVersion,
          editable,
          metadata,
          files
        };
      }

      // UI CODE

      document.querySelector("#gex").addEventListener("change", async (ev) => {
        if (ev.target.files.length === 1) {
          const fileContents = new Uint8Array(
            await ev.target.files[0].arrayBuffer()
          );
          const gex = await decompile(fileContents);
          console.log({ gex });
          document.querySelector("#metadata").innerText = JSON.stringify(
            gex,
            (k, v) => { 
              if(k === "dataText")
              {
                return undefined;
              }
              return (v instanceof Uint8Array) ? "Uint8Array(" + v.length + ")" : v
            },
            2
          );
          
          
          document.querySelector("#files").innerHTML = "";
          for(const file of gex.files)
          {
            const node = document.querySelector("#dat-file").content.cloneNode(true)
            node.querySelector("h4").innerText = file.fileName;
            node.querySelector("textarea").value = file.dataText;
            
            node.querySelector("a").href = URL.createObjectURL( new Blob([file.data]));
            node.querySelector("a").innerText = "Download " + file.fileName;

            document.querySelector("#files").appendChild(node);
          }
        }
      });
    </script>
    <template id="dat-file">
      <div>
        <h4></h4>
        <a href="#" download>Download File</a><br/>
        <textarea rows="40" cols="80"></textarea>
      </div>
    </template>
    <h2>Metadata</h2>
    <pre id="metadata"></pre>
    <h3>DAT file contents</h3>
    <div id="files">

    </div>
    
  </body>
 </html>
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1.0" />
	<title>GameMaker 7/8.1 GEX decompiler</title>
	</head>
	<body>
	<h1>GameMaker 7/8.1 GEX decompiler</h1>
	<p>
	<strong>What the hell is this?</strong>
	<br/>
	I found a GameMaker 8.1 project of mine, and wanted to open it in Game Maker Studio 2.0.<br/>
	You can't natively import <code>.gmk</code> files into GMS2. <br/>
	I used <a href="http://lateralgm.org/">LateralGM</a> to get the project into a GMS1 compatible format.
	<br/><br/>
	Unfortunately this doesn't seem to handle extension packages. (A mechanism for reusable code)<br/>
	And GMS1/2 doesn't handle <code>.gex</code> files.<br/>
	So, I wrote this decompiler to get the code out of a <code>.gex</code> file so I could get the project to compile in GMS2.
	</p>

	<p>
	<strong>References I used in building this.</strong><br/>
	<a href="https://enigma-dev.org/docs/Wiki/GMKrypt">https://enigma-dev.org/docs/Wiki/GMKrypt</a><br/>
	<a href="http://lateralgm.org/formats/gmkrypt1.html">http://lateralgm.org/formats/gmkrypt1.html</a><br/>
	<a href="https://github.com/IsmAvatar/LateralGM">https://github.com/IsmAvatar/LateralGM</a><br/>
	<a href="https://enigma-dev.org/docs/Wiki/GEX_format">https://enigma-dev.org/docs/Wiki/GEX_format</a><br/>
	<a href="https://enigma-dev.org/docs/Wiki/GED_format">https://enigma-dev.org/docs/Wiki/GED_format</a><br/>
	</p>
	<p>
	This madness is all <a href="https://develop.games/" target="_blank">Thor's fault.</a>
	</p>
	<hr/>
	<input type="file" id="gex" accept=".gex" />

	<script type="module">
	// This code only exists because Thor is a meance of postivity towards making games.

	// GMKrypyt code
	// https://enigma-dev.org/docs/Wiki/GMKrypt
	// http://lateralgm.org/formats/gmkrypt1.html

	function generateSwapTable(seed) {
	const table = [[], []]; // int[][] table = new int[2][256];

	const a = 6 + (seed % 250);
	const b = Math.floor(seed / 250);

	for (let i = 0; i < 256; i++) {
	table[0][i] = i;
	}

	for (let i = 1; i < 10001; i++) {
	const j = 1 + ((i * a + b) % 254);
	const t = table[0][j & 0xff];
	table[0][j] = table[0][j + 1] & 0xff;
	table[0][j + 1] = t & 0xff;
	}
	table[1][0] = 0; //this operation is optional, as 0 is default
	for (let i = 1; i < 256; i++) {
	table[1][table[0][i]] = i & 0xff;
	}
	return table;
	}

	export function decryptGMKrypt(seed, data) {
	const lookup = generateSwapTable(seed);

	return data.map((byte) => lookup[1][byte] & 0xff);
	}

	// GEX File format decompiler
	// https://github.com/IsmAvatar/LateralGM
	// https://enigma-dev.org/docs/Wiki/GED_format#cite_note-extdef-1
	export async function decompile(data) {
	const view = new DataView(data.buffer);

	const formatId = view.getInt32(0, true);
	const version = view.getInt32(4, true);

	// const seedPre = view.getInt32(8, true);
	// const seedPost = view.getInt32(12, true);

	const seed = view.getInt32(8, true);

	const plaintext = decryptGMKrypt(seed, data.slice(12));
	// Parse the GED
	const txtDec = new TextDecoder();

	const plainView = new DataView(plaintext.buffer);

	function readPrefixedString() {
	const size = plainView.getUint32(gedOffset, true);
	const value = txtDec.decode(
	plaintext.subarray(gedOffset + 4, gedOffset + 4 + size)
	);
	gedOffset += 4 + size;
	return value;
	}

	function readUInt32() {
	const value = plainView.getUint32(gedOffset, true);
	gedOffset += 4;
	return value;
	}
	let gedOffset = 0;

	const gedVersion = readUInt32();
	const editable = readUInt32();

	const labels = [
	"Name",
	"Folder",
	"Version",
	"Author",
	"Date",
	"License",
	"Description",
	"Help File",
	];
	const metadata = {};

	for (const label of labels) {
	const value = readPrefixedString();
	metadata[label] = value;
	}

	const hidden = readUInt32(); // Skip hidden

	// Uses
	const usesCount = readUInt32();
	const uses = [];
	for (let i = 0; i < usesCount; i++) {
	uses.push(readPrefixedString());
	}

	// Files
	const filesCount = readUInt32();
	const files = [];
	const fileTypes = ["N/A", "DLL", "gml", "Action Library", "Other"];
	const callCon = { 2: "GML", 11: "stdCall", 12: "cdecl" };
	for (let i = 0; i < filesCount; i++) {
	const version = readUInt32();

	const fileName = readPrefixedString();

	const originalName = readPrefixedString();

	const kind = fileTypes[readUInt32()];

	const initialization = readPrefixedString();

	const finalization = readPrefixedString();

	const functionCount = readUInt32();

	const functions = [];
	for (let i = 0; i < functionCount; i++) {
	const version = readUInt32();
	const name = readPrefixedString();
	const ext_name = readPrefixedString();
	const call_con = callCon[readUInt32()];
	const helpLine = readPrefixedString();
	const hidden = readUInt32();
	const argCount = readUInt32();

	gedOffset += 4 * 18;

	functions.push({
	version,
	name,
	ext_name,
	call_con,
	helpLine,
	hidden,
	argCount,
	});
	}

	const constantCount = readUInt32();

	const constants = [];
	for (let i = 0; i < constantCount; i++) {
	const version = readUInt32();
	const name = readPrefixedString();
	const value = readPrefixedString();
	const hidden = readUInt32();
	constants.push({
	version,
	name,
	value,
	hidden,
	});
	}

	files.push({
	version,
	fileName,
	originalName,
	kind,
	initialization,
	finalization,
	functions,
	constants,
	});
	}

	async function readCompressedDat()
	{
	const datSize = readUInt32();
	const datCompressed = plaintext.slice(gedOffset, gedOffset + datSize);
	gedOffset += datSize;

	const unzip = new DecompressionStream("deflate");
	const writer = unzip.writable.getWriter();
	writer.write(datCompressed);
	writer.releaseLock();

	const reader = unzip.readable.getReader();

	const read = await reader.read();
	return read.value;
	}

	for(let file of files)
	{
	file.data = await readCompressedDat();
	file.dataText = txtDec.decode(file.data);
	}

	console.log({
	gedVersion,
	editable,
	hidden,
	metadata,
	files
	});



	// const datSeed = readUInt32();
	// console.log("datSeed:", datSeed);

	// console.log( gedOffset + datSize , plaintext.length);


	// console.log(unzip.length);

	return {
	gedVersion,
	editable,
	metadata,
	files
	};
	}

	// UI CODE

	document.querySelector("#gex").addEventListener("change", async (ev) => {
	if (ev.target.files.length === 1) {
	const fileContents = new Uint8Array(
	await ev.target.files[0].arrayBuffer()
	);
	const gex = await decompile(fileContents);
	console.log({ gex });
	document.querySelector("#metadata").innerText = JSON.stringify(
	gex,
	(k, v) => {
	if(k === "dataText")
	{
	return undefined;
	}
	return (v instanceof Uint8Array) ? "Uint8Array(" + v.length + ")" : v
	},
	2
	);


	document.querySelector("#files").innerHTML = "";
	for(const file of gex.files)
	{
	const node = document.querySelector("#dat-file").content.cloneNode(true)
	node.querySelector("h4").innerText = file.fileName;
	node.querySelector("textarea").value = file.dataText;

	node.querySelector("a").href = URL.createObjectURL( new Blob([file.data]));
	node.querySelector("a").innerText = "Download " + file.fileName;

	document.querySelector("#files").appendChild(node);
	}
	}
	});
	</script>
	<template id="dat-file">
	<div>
	<h4></h4>
	<a href="#" download>Download File</a><br/>
	<textarea rows="40" cols="80"></textarea>
	</div>
	</template>
	<h2>Metadata</h2>
	<pre id="metadata"></pre>
	<h3>DAT file contents</h3>
	<div id="files">

	</div>

	</body>
	</html>